Sound measuring



June 12, 1928. I 1,673,037'

D.G.BLATTNER' SOUND MEASURING Filed March 22, 1926 Patented June 12,1928.

UNITED STATES 1,673,037 PATENT oFF-ica.

DAVID G. BLA'ITNER, OF BOGOTA, NEW JERSEY, ASSIGNOR T BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW roan.

SOUND MEASURING.

Applicationflled March 22, 1926. Serial No. 93,481.

This invention relates to a sound or noise measuring device and a method of measuring the amount of noise emanating from a given source.

5 In certain mechanical systems, where there are moving parts, the noise maybe such as to cause considerable annoyance to either the user or people in the proximity. This is especially true in the higher class automobiles where noiselessness of operation is a very desirable characteristic and is one of the problems which automobile engineers are continually attempting to solve.

The object of this invention is to provide 1 for an indication of or the determination of the amount of sound or noise from a given source, as, for instance, a bearing.

In carryin out this object there is preferably provi ed an ordinary listening stick in one end of which is mounted a telephone receiver. This receiver is in circuit with a source of electrical power of desired frequency components to actuatethe telephone receiver, the amount of power 1n the receiver being readily variable at will. It is well known from a study of acoustics thatone sound may mask another sound and that such maskin is dependent, to a certain extent, upon 1: e frequency and intensity of the so masked andmasking sounds, the intensity, however, being the predominate factor- In carrfi'tng out this. invention this principle of 'mas g is made use of, the noise or sound from the source to be investigated being used as to mask the sound from a known source. A comparison of the electrical ower supplied to the receiver when the sound from it is just masked by the noise from the noise source,

- with the electrical power supplied to the 0 receiver to cause the sound therein to be just inaudible when no other noise is present gives a measure of the noise from-the noise source,

The attached drawing shows a preferred form of listenin stick and the apparatus used with it an the following description covers this referred form.

The stan ard source of power the out at from which can be measured is shown so ematically at 10, and includes a battery 11,

buzzer 12, condensers 13 and resistances 15..

An attenuator 16 regulates the 'wer deliv ered to the telephone receiver, 1s apparatus forms what is commonly known as an I pointed end of the stic audiometer, which is well known in the art.

The listening stick consists of a rod 17, one end of which is pointed and if desired may be metal tipped. The other end of the stick is cup shaped, as shown, and mounted in this end is a telephone receiver 18, preferably of the watch case type. The receiver is connected to the audiometer through conductors 19 and transforms the electrical power re ceived through this medium into sound energy.

It is understood that the masked tone is developed by the telephone receiver and that the noise to be measured, that is the masking tone, is developed in the ear by the vibration of one or more movin parts to which the 1s" applied. 1 In operation, the listening stick and audiometer are taken to a room in which no per ceptible sound exists. The audiometer is then adjusted until the sound produced by the receiver 18 is just imperceptible. The whole device is then taken to the source of the noise to be studied and the pointed end of the stick is applied .to the surface or part from which the noise emanates. Again the 0 audiometer is adjusted until the soundproduced in the receiver is just imperceptible. It has been determined that when usin the listening device in this manner the sound power supplied by the receiver is less than the power supplied fromthe noise source, by a su stantially constant factor, which'may be determined by trial. Further, the sound power intensity from the ,ieceiver' is proportional to the electrical power input thereto to, so that the acoustic noise] power bears a constant'relation to the electrical power input to the receiver. i

The attenuator iscalibrated in units loss, that is, with a known amount of power out put from the buzzer, themaximum loss or ighest reading on the attenuator scale pro-v duces in the receiver the least sound. As the sound from the receiver is increased, the scale reading becomes less since there is less loss. From this it follows that, if'the setting of the attenuator in the quiet room is X and the settin when the listening stick is ap lied to the noise source is Y and the mas ng constant is A, the intensity B from the noise will be X- Y+A. The attenuator may be calibrated in any arbitrary unit as long as the constant factor A is in the same unit.

It has been found, however, in practice that it is convenient to use the transmission umt 1 represented by TU which is used quite unitill versally in telephone practice;

While the embodiment of the invention herein described involves the use of a listening stick anda telephone receiver,the invention in its broader aspects, as expressed in certain of the appended claims may obviously be carried out with other instrumentalities.

What is claimed is:

1. In combination, an element capable of transmitting sound and adapted to be ap plied to the ear, a source of controllable wave energy for setting up sound waves 1n said element, means for decreasing'the amplitude of said sound waves until the threshold of audibilitv is reached, and means for transmitting energy from'a source of sound to be investigated to said element simultancr ously with thesetting up therein of the controllable sound.

2, In combination, an element capable of transmitting sound and adapted to be applied to the ear, a source of controllable electric'al wave energy for setting up sound waves in said element, means for decreasing the amplitude of said sound waves until the threshold of audibility is reached,'and means for mechanically transmittin sound from a source of sound to be investigated to said element simultaneously with the setting up therein of the controllable sound.

3, in combination, a listening stick, one end of which is adapted to" be applied to a noise or sound source and the other end of which is adapted to be applied to the ear, and. means for producing at the end of the sticlr to which the ear is applied, a sound independent of that from the noise or sound source, a a

l. In combination, a listening stick, one end of which is adapted to be applied to a noise or sound source to be investigated, the other end of whichis adapted. to be applied to the earl means for producing at the end of the stick to which the ear is applied, .a sound, independent of that from the source to be investigated, and means to vary the intensity of the sound produced by said means to permit a comparison oi the two sources;

5. In a sound measuring device, a listenmg stick having one end adapted to be a plied to a noise or sound source to be investi source, utilizing a listening 1 pulses, said impulses being audiblewhen applied to said receiver, and means to vary the intensity of-said impulses to permit comparison of the two sources,

6. In a sound measuring device, a listening stick having'one end pointed so as to be readily applied to a noise or sound produeing source to be investigated and having the other end cup-shaped and arranged to be applied to the car, a telephone receiver mounted in said cup-shaped portion, a source of electrical impulses connected to said receiver, said impulses being made audible therein, and means to vary the intensityof the sound in said receiver produced by said electrical impulses to permit a comparison of the sounds from the two sources.

7. A method of obtaining an indication of the amount of sound emanating from a noise or sound source which comprises utireceiver mounted in the stcning end in which a controllable sound may be produced,

said method comprising obtaining an indication of the energy supplied to the receiver when the controllable sound only is present and is just at the threshold of audibility and 9 obtaining a second indication of the energy supplied to the receiver when the sound therein is just masked by tllQIlOlSQ from the noise source;

9. in combination, an element capable of transforming electrical power to. acoustic power and adapted to be applied to the ear, a source of electrical power suitable for transformation to acoustic power by said element, means for decreasing the intensity of said acousticpower until the threshold of audibility' is reached, and means for trans mitting energy from a source of sound to be investigated through said element to the ear its simultaneously with the setting up therein of the controllable sound. p in witness whereof, I hereunto subscribe my name this 19th day of March, A, D,

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